Moon Footprints Will Be Covered Up Much Sooner Than Expected

On July 20, 1969, Neil Armstrong planted the first human foot on the Moon and uttered his famous words. “That’s one small step for a man, one giant leap for mankind.” His footprints along with his fellow Apollo astronauts are still there more than 40 years later. And will be there for countless years to come.

But new research says these footprints will be gone much sooner than expected.

Armstrong’s footprints are still undisturbed because there isn’t any force on the moon that can change its surface quickly. No wind or water means no erosion. No volcanic activity means no resurfacing. There are two ways the moon’s surface can change. One of them is fast. The other is slow. Very slow.

Meteorites can change the surface in an instant. But the chances of a particular location seeing an impact is slim. Solar wind can also change the surface of the moon, but that process is excruciatingly slow.

This week’s research focuses on meteorites. Specifically, how often they impact the lunar surface.

Before LRO began observing the lunar surface, scientists believed “that churning of the lunar regolith (soil) from meteoroid impacts typically took millions of years to overturn the surface down to 2 centimeters,” said lead author Emerson Speyerer. Lunar craters formed in the past few years suggest this is occurring much faster.

“The newly determined churning rate means that the Apollo astronaut tracks will be gone in tens of thousands of years rather than millions,” added co-author Mark Robinson.

Let’s take a look at a fresh lunar crater.

This crater is believed to have formed sometime between October 2012 and April 2013. Its crater is about 40 feet in diameter, but the image shows an area more than 4,000 feet wide. See all the black stuff? That’s material originating from the impact. And it’s blasted much further away from the crater than researchers calculated in previous models.

Not only was material blasted further away from the crater, but LRO observations showed 30% more new craters than expected compared to cratering models.

“With this potentially higher impact rate, features with young model ages derived using crater counts and the standard rate may in fact be even younger than previously thought,” said Speyerer. “However, to be certain, we need several more years of observations and new crater discoveries.”

It wasn’t just the direct impacts themselves causing surface changes. Speyerer and his colleagues noted more than 47,000 other small changes on the lunar surface. The team believes they are secondary changes caused as material is thrown up from the initial impact and hits the surface again (dubbed splotches).

The new churning rate, with splotch formation included, would overturn 2 centimeters of nearly all of the lunar surface (99%) in 81,000 years.

This week’s research also has implications for a lunar base. “The increased churning rate will be important information for future designers of moon bases, said Speyerer. “Surface assets will have to be designed to withstand impacts from small particles moving at up to 500 meters per second (about 1,600 feet per second or 1,100 miles per hour).”

The chances of an impact by a single meteorite is remote. But the material thrown up from a nearby impact? That could happen much more frequently and it will be something lunar base designers will have to account for.

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